//
// Code from "How to: Implement an Expression Tree Visitor" article on MSDN
// http://msdn.microsoft.com/en-us/library/bb882521.aspx
//

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq.Expressions;

namespace NAom.DAL
{
  internal abstract class ExpressionVisitor
  {

    protected virtual Expression Visit(Expression exp)
    {
      if (exp == null)
        return exp;
      switch (exp.NodeType)
      {
        case ExpressionType.Negate:
        case ExpressionType.NegateChecked:
        case ExpressionType.Not:
        case ExpressionType.Convert:
        case ExpressionType.ConvertChecked:
        case ExpressionType.ArrayLength:
        case ExpressionType.Quote:
        case ExpressionType.TypeAs:
          return this.VisitUnary((UnaryExpression)exp);
        case ExpressionType.Add:
        case ExpressionType.AddChecked:
        case ExpressionType.Subtract:
        case ExpressionType.SubtractChecked:
        case ExpressionType.Multiply:
        case ExpressionType.MultiplyChecked:
        case ExpressionType.Divide:
        case ExpressionType.Modulo:
        case ExpressionType.And:
        case ExpressionType.AndAlso:
        case ExpressionType.Or:
        case ExpressionType.OrElse:
        case ExpressionType.LessThan:
        case ExpressionType.LessThanOrEqual:
        case ExpressionType.GreaterThan:
        case ExpressionType.GreaterThanOrEqual:
        case ExpressionType.Equal:
        case ExpressionType.NotEqual:
        case ExpressionType.Coalesce:
        case ExpressionType.ArrayIndex:
        case ExpressionType.RightShift:
        case ExpressionType.LeftShift:
        case ExpressionType.ExclusiveOr:
          return this.VisitBinary((BinaryExpression)exp);
        case ExpressionType.TypeIs:
          return this.VisitTypeIs((TypeBinaryExpression)exp);
        case ExpressionType.Conditional:
          return this.VisitConditional((ConditionalExpression)exp);
        case ExpressionType.Constant:
          return this.VisitConstant((ConstantExpression)exp);
        case ExpressionType.Parameter:
          return this.VisitParameter((ParameterExpression)exp);
        case ExpressionType.MemberAccess:
          return this.VisitMemberAccess((MemberExpression)exp);
        case ExpressionType.Call:
          return this.VisitMethodCall((MethodCallExpression)exp);
        case ExpressionType.Lambda:
          return this.VisitLambda((LambdaExpression)exp);
        case ExpressionType.New:
          return this.VisitNew((NewExpression)exp);
        case ExpressionType.NewArrayInit:
        case ExpressionType.NewArrayBounds:
          return this.VisitNewArray((NewArrayExpression)exp);
        case ExpressionType.Invoke:
          return this.VisitInvocation((InvocationExpression)exp);
        case ExpressionType.MemberInit:
          return this.VisitMemberInit((MemberInitExpression)exp);
        case ExpressionType.ListInit:
          return this.VisitListInit((ListInitExpression)exp);
        default:
          throw new Exception(string.Format("Unhandled expression type: '{0}'", exp.NodeType));
      }
    }

    protected virtual MemberBinding VisitBinding(MemberBinding binding)
    {
      switch (binding.BindingType)
      {
        case MemberBindingType.Assignment:
          return this.VisitMemberAssignment((MemberAssignment)binding);
        case MemberBindingType.MemberBinding:
          return this.VisitMemberMemberBinding((MemberMemberBinding)binding);
        case MemberBindingType.ListBinding:
          return this.VisitMemberListBinding((MemberListBinding)binding);
        default:
          throw new Exception(string.Format("Unhandled binding type '{0}'", binding.BindingType));
      }
    }

    protected virtual ElementInit VisitElementInitializer(ElementInit initializer)
    {
      ReadOnlyCollection<Expression> arguments = this.VisitExpressionList(initializer.Arguments);
      if (arguments != initializer.Arguments)
      {
        return Expression.ElementInit(initializer.AddMethod, arguments);
      }
      return initializer;
    }

    protected virtual Expression VisitUnary(UnaryExpression u)
    {
      Expression operand = this.Visit(u.Operand);
      if (operand != u.Operand)
      {
        return Expression.MakeUnary(u.NodeType, operand, u.Type, u.Method);
      }
      return u;
    }

    protected virtual Expression VisitBinary(BinaryExpression b)
    {
      Expression left = this.Visit(b.Left);
      Expression right = this.Visit(b.Right);
      Expression conversion = this.Visit(b.Conversion);
      if (left != b.Left || right != b.Right || conversion != b.Conversion)
      {
        if (b.NodeType == ExpressionType.Coalesce && b.Conversion != null)
          return Expression.Coalesce(left, right, conversion as LambdaExpression);
        else
          return Expression.MakeBinary(b.NodeType, left, right, b.IsLiftedToNull, b.Method);
      }
      return b;
    }

    protected virtual Expression VisitTypeIs(TypeBinaryExpression b)
    {
      Expression expr = this.Visit(b.Expression);
      if (expr != b.Expression)
      {
        return Expression.TypeIs(expr, b.TypeOperand);
      }
      return b;
    }

    protected virtual Expression VisitConstant(ConstantExpression c)
    {
      return c;
    }

    protected virtual Expression VisitConditional(ConditionalExpression c)
    {
      Expression test = this.Visit(c.Test);
      Expression ifTrue = this.Visit(c.IfTrue);
      Expression ifFalse = this.Visit(c.IfFalse);
      if (test != c.Test || ifTrue != c.IfTrue || ifFalse != c.IfFalse)
      {
        return Expression.Condition(test, ifTrue, ifFalse);
      }
      return c;
    }

    protected virtual Expression VisitParameter(ParameterExpression p)
    {
      return p;
    }

    protected virtual Expression VisitMemberAccess(MemberExpression m)
    {
      Expression exp = this.Visit(m.Expression);
      if (exp != m.Expression)
      {
        return Expression.MakeMemberAccess(exp, m.Member);
      }
      return m;
    }

    protected virtual Expression VisitMethodCall(MethodCallExpression m)
    {
      Expression obj = this.Visit(m.Object);
      IEnumerable<Expression> args = this.VisitExpressionList(m.Arguments);
      if (obj != m.Object || args != m.Arguments)
      {
        return Expression.Call(obj, m.Method, args);
      }
      return m;
    }

    protected virtual ReadOnlyCollection<Expression> VisitExpressionList(ReadOnlyCollection<Expression> original)
    {
      List<Expression> list = null;
      for (int i = 0, n = original.Count; i < n; i++)
      {
        Expression p = this.Visit(original[i]);
        if (list != null)
        {
          list.Add(p);
        }
        else if (p != original[i])
        {
          list = new List<Expression>(n);
          for (int j = 0; j < i; j++)
          {
            list.Add(original[j]);
          }
          list.Add(p);
        }
      }
      if (list != null)
      {
        return list.AsReadOnly();
      }
      return original;
    }

    protected virtual MemberAssignment VisitMemberAssignment(MemberAssignment assignment)
    {
      Expression e = this.Visit(assignment.Expression);
      if (e != assignment.Expression)
      {
        return Expression.Bind(assignment.Member, e);
      }
      return assignment;
    }

    protected virtual MemberMemberBinding VisitMemberMemberBinding(MemberMemberBinding binding)
    {
      IEnumerable<MemberBinding> bindings = this.VisitBindingList(binding.Bindings);
      if (bindings != binding.Bindings)
      {
        return Expression.MemberBind(binding.Member, bindings);
      }
      return binding;
    }

    protected virtual MemberListBinding VisitMemberListBinding(MemberListBinding binding)
    {
      IEnumerable<ElementInit> initializers = this.VisitElementInitializerList(binding.Initializers);
      if (initializers != binding.Initializers)
      {
        return Expression.ListBind(binding.Member, initializers);
      }
      return binding;
    }

    protected virtual IEnumerable<MemberBinding> VisitBindingList(ReadOnlyCollection<MemberBinding> original)
    {
      List<MemberBinding> list = null;
      for (int i = 0, n = original.Count; i < n; i++)
      {
        MemberBinding b = this.VisitBinding(original[i]);
        if (list != null)
        {
          list.Add(b);
        }
        else if (b != original[i])
        {
          list = new List<MemberBinding>(n);
          for (int j = 0; j < i; j++)
          {
            list.Add(original[j]);
          }
          list.Add(b);
        }
      }
      if (list != null)
        return list;
      return original;
    }

    protected virtual IEnumerable<ElementInit> VisitElementInitializerList(ReadOnlyCollection<ElementInit> original)
    {
      List<ElementInit> list = null;
      for (int i = 0, n = original.Count; i < n; i++)
      {
        ElementInit init = this.VisitElementInitializer(original[i]);
        if (list != null)
        {
          list.Add(init);
        }
        else if (init != original[i])
        {
          list = new List<ElementInit>(n);
          for (int j = 0; j < i; j++)
          {
            list.Add(original[j]);
          }
          list.Add(init);
        }
      }
      if (list != null)
        return list;
      return original;
    }

    protected virtual Expression VisitLambda(LambdaExpression lambda)
    {
      Expression body = this.Visit(lambda.Body);
      if (body != lambda.Body)
      {
        return Expression.Lambda(lambda.Type, body, lambda.Parameters);
      }
      return lambda;
    }

    protected virtual NewExpression VisitNew(NewExpression nex)
    {
      IEnumerable<Expression> args = this.VisitExpressionList(nex.Arguments);
      if (args != nex.Arguments)
      {
        if (nex.Members != null)
          return Expression.New(nex.Constructor, args, nex.Members);
        else
          return Expression.New(nex.Constructor, args);
      }
      return nex;
    }

    protected virtual Expression VisitMemberInit(MemberInitExpression init)
    {
      NewExpression n = this.VisitNew(init.NewExpression);
      IEnumerable<MemberBinding> bindings = this.VisitBindingList(init.Bindings);
      if (n != init.NewExpression || bindings != init.Bindings)
      {
        return Expression.MemberInit(n, bindings);
      }
      return init;
    }

    protected virtual Expression VisitListInit(ListInitExpression init)
    {
      NewExpression n = this.VisitNew(init.NewExpression);
      IEnumerable<ElementInit> initializers = this.VisitElementInitializerList(init.Initializers);
      if (n != init.NewExpression || initializers != init.Initializers)
      {
        return Expression.ListInit(n, initializers);
      }
      return init;
    }

    protected virtual Expression VisitNewArray(NewArrayExpression na)
    {
      IEnumerable<Expression> exprs = this.VisitExpressionList(na.Expressions);
      if (exprs != na.Expressions)
      {
        if (na.NodeType == ExpressionType.NewArrayInit)
        {
          return Expression.NewArrayInit(na.Type.GetElementType(), exprs);
        }
        else
        {
          return Expression.NewArrayBounds(na.Type.GetElementType(), exprs);
        }
      }
      return na;
    }

    protected virtual Expression VisitInvocation(InvocationExpression iv)
    {
      IEnumerable<Expression> args = this.VisitExpressionList(iv.Arguments);
      Expression expr = this.Visit(iv.Expression);
      if (args != iv.Arguments || expr != iv.Expression)
      {
        return Expression.Invoke(expr, args);
      }
      return iv;
    }
  }
}
